What do you do after inventing the iPod? Steve Jobs and Apple may have got all the credit for building the product that led to the all-conquering iPhone and iPad, but it was Tony Fadell who touted his plan for an MP3 player round various companies, tried Real Networks first and approached Apple in 2001. So Fadell’s next challenge is… thermostats. Could anything be less sexy?

Fadell is keen to talk about Nest, his thermostat for a smartphone generation. It learns your habits and adjusts your energy usage accordingly. Ten million Americans alone replace their thermostats each year; a man who by his own admission “doesn’t need to work again” has built a team of other Silicon Valley millionaires and is working on a market sector he says is “bigger than refrigerators, bigger than video games”.

But isn’t everyone much more interested in Apple, not least because no former executive ever talks about the secretive, multi-billion dollar market leader? Yet Fadell – perhaps it’s to promote Nest – isn’t shy of talking about his former employer. It’s an in-joke among journalists that there’s no difference between talking to Apple employees past or present, on or off the record because there’s never a story. But Fadell talks as though there’s nothing he wouldn’t say.

So what of the visionary company – whose own mythology implies it built the iPod in order to build the iPhone, and saw a future of apps and touchscreens. “That’s b-------,” says Fadell. “It’s revisionist history. And Apple can do it because they never say anything, right?”

Fadell says his team at Apple was leading a tiny experiment. “When I showed the iPod to Steve and he said ‘It’s a go’ he meant to the next milestone. He didn’t mean we were going to even ship it. This is a company whose business was the Macintosh. It wasn’t as if there’d been this big decision to suddenly turn this way,” he claims. “We wanted to do everything at the cutting edge to the very best of our ability, but we didn’t have this grand idea.” Fadell says that even the iPod team he built was largely taken up with “the day job” of building the Macintosh. Apple, after all, was a company with $500m of debt at the time. “It couldn’t have been more different from the Apple of today,” says Fadell.

The former iPod boss - he left in 2008 - is keen to ask and answer the question “Is Apple a visionary company today? Absolutely. Does it build amazing products? Absolutely.” But at the same time he is unequivocal: at the beginning “there was no vision of taking everything to a world of iPhones and iPads”.

And what about the genius of Steve Jobs then? Obviously, it’s not in Fadell’s interest to agree to the hagiography that says Jobs changed every detail of every product, because that would imply his own Nest thermostat might not be perfect. But he makes a good case for his own product design credentials. “We built the iPod in weeks. It had to be what I thought it was going to be because there wasn’t time for endless refinements”. According to Fadell, there was an iPod visionary. He just doesn’t say it was Steve Jobs.

He never suggests, however, that the iPod wasn’t a product of a unique culture. He says he grew up in the atmosphere that produced the Macintosh in Silicon Valley and cocnedes he owes a huge debt to Jobs and Apple. “I’d absolutely heard all the Steve stories,” he says. “The guys I worked with in those businesses were key to making the products we shipped later.”

Fadell is also happy, however, to explain Apple’s unique approach to PR, which has built a brand that detractors decry as style over substance yet promotes unprecedented loyalty among its fans. “If you’re a company focused on competitors,” he says, “you’ll be a follower. And you’ll talk to the media about all sorts of stuff. But if you’re a company focused on the consumer you’ll talk about the products that you’ve got and how to get the most out of them. But you won’t talk about what’s coming and you won’t talk about strategy. Consumers are interested in products.” Plus, he adds, when you’re as enormous as Apple, you can’t practically talk to everyone anyway.

Fadell is clear that Apple made the iPod and the iDevices what they are. “Without the computing platform of Apple, it could all have been swallowed up by a Sony and we wouldn’t be where we are, “ he says.

Growth has left Apple “less nimble” Fadell concedes, but visionary nonetheless. “Usually the biggest companies are not the most dynamic”, he says.

For him, however, the wealth Apple brought has been tempered by what he calls “an idea burning in his brain” and the desire to work in order to “be a role model to my kids”. It would, he says, have been hard to tell his children that work was a good thing to do if he didn’t do it himself.

Fadell is in the UK this week to talk about launching Nest outside the US and Canada. Consumers in more than 60 other countries have already made it work outside those supported areas (a difficult feat), but, like Apple, he’s not keen to talk about future plans.

What he is willing to say is that he believes the size of the energy market makes it ripe for disruption, especially in deregulated Britain. He says he looked around his home for the things that “didn’t make sense for the smartphone generation”. “I started designing the greenest the most connected home, before the iPhone and the iPad,” he says. “I knew it was coming, and I thought how does this change.”

Nest gives information on heating or cooling for each zone in a house, detailed data on energy use and learns when users aren’t there to predict their behaviour. Fadell talks about 20 per cent market share. “Investors were calling me saying we want to give you money,” he says, adding “that’s not a common problem.”

The Nest looks neat, makes everything easier, cheaper, and greener. If Steve Jobs convinced every teenager in the western world they needed an iPod, then Fadell is going after an even bigger, wealthier market: the people who pay the heating bills. And today hose people are the iPod generation.